The present invention relates to a pattern defect inspection apparatus, particularly, to an apparatus for inspecting defects of the photomask used in the manufacture of a semiconductor device and the pattern of the semiconductor wafer or for inspecting the defects of the pattern of a liquid crystal display substrate.
A defect of the photomask used in the manufacture of a semiconductor device by means of photolithography is one of the main reasons for the reduction in the yield of a large-scale integrated circuit (LSI). To overcome the difficulty, vigorous studies are being made in an attempt to develop an apparatus for inspecting the defect of the photomask.
The conventional mask defect inspection apparatus is roughly classified into a type in which two chips having the same pattern written therein are independently detected and observed, and the difference therebetween is compared by a suitable defect detecting means so as to detect the defect, and another type in which a pattern and a design data are compared by a defect detecting means so as to detect the defect. The former type is advantageous in that a design data is not required because the two chips having the same pattern written therein are separately observed and compared by different detecting means. However, the former type is unsatisfactory in that the same pattern is required to be formed in a plurality of regions of a single mask, with the result that a defect cannot be detected by comparison of the patterns formed in the mask. On the other hand, the latter type requires a design pattern used for comparison, leading to a complex circuit construction. However, since the defect is detected by comparison with the design pattern, a highly strict inspection can be achieved. In addition, the inspection can be performed even if only one pattern is formed in a single mask.
Where a defect has been found in the conventional inspection apparatus outlined above, the information such as the defective point and the coordinate position of the defective point are stored by some method, e.g., stored in a magnetic disk, and a review treatment is carried out after completion of the inspection over the entire region. The operator visually inspects the defective portion and judges whether a re-repair is required so as to transfer the inspected object to a repairing process, as required. Where repair is performed, the operator determines whether to perform a white defect repair for making up for a defective point or a black defect repair for deleting an extruding defect.
FIGS. 1A and 1B schematically exemplify a mask pattern and a defect thereof. A portion in a stripe of an inspection stripe shown in FIG. 1B is schematically shown in a magnified fashion in FIG. 1A. A shaded portion in FIG. 1A denotes a chromium portion (light shielding portion) of a mask 2, with a white portion representing a glass portion (transparent portion) of the mask 2. Portions A and B shown in the drawing denote defects of a standard size, e.g., about 0.2 to 2 .mu.m, which can be repaired. Many of the defects are occupied by the defects of the standard size. On the other hand, it is difficult to repair portion C in which a large portion, e.g., on the order of 10 .mu.m to 100 .mu.m, of the chromium region is omitted. Such a large defect as cannot be repaired rarely takes place. However, the presence of such a large defect, even if only one defect is present, makes the mask quite unusable so as to be discarded.
In general, the mask is automatically inspected. After inspection on the entire region of a single mask, it is judged whether to repair the defect based on confirmation of the presence or absence of the defect and the type of the defect such as the lack of chromium, residue of chromium and dust (review treatment). A series of these operations take about one hour even where the operations are simple and 5 to 6 hours or more in some cases. Where such a large defect as not to be repaired is found unfortunately at the final stage of the operation, all the time spent up to then is rendered quite insignificant.
As described above, the review treatment is performed after inspection on the entire region of the mask in the conventional pattern defect inspection apparatus, with the result that it is impossible to know the presence of a large defect, which makes the mask unusable, until completion of the inspection over the entire region. In the manufacture of the up-to-date mask of this kind, it is important to shorten the turn-around time as much as possible. It should be noted that, if the presence of a large defect can be detected in an early stage, it is possible to take measures against the defect occurrence promptly or to make a quick decision to manufacture again the mask, with the result that the turn-around time can be shortened as a whole. Also, since an extra operation need not be carried out, the inspection system is enabled to perform its operation efficiently, leading to an improved productivity.